What's interesting is that HP Autowerks also saw a 15ish who gain on their 1M when they switched out the midpipes and Borla catback muffler. I wonder if the N54 midpipes are as restrictive as everyone thinks.

That is interesting. I went back and found the post and they are running GAIC stage 1 tune so the two cars are reasonably apples to apples. Honestly, even less restricted back pressure from the free flow midpipes probably doesn't matter until you get into the stage 2 level of tune. Then you are running an FMIC as well and increasing the boost pressure through out the entire system.

Possibly with a stage 1 level of tune you reach a certain level of reduced back pressure and anything less than that doesn't create extra hp. Not certain if this is right or not, just thinking (typing) out loud here. Seems reasonably plausible though..